Pressure-regulating control mechanism



Dec. 14, 1948. N. c, PRECE 2,456,215

PRESSURE REGULATING CONTROL MECHANISM Original Filed June 27, 1938 E '1mi 1 TSnvmtor Nathan C. Rice @WIQMM Ottoman Patented Dec. 14, 1948PRESSURE-REGULATING CONTROL MECHANISM Nathan C. Price, Hollywood,Calif., assignor to Boeing Airplane Company, a corporation of DelawareOriginal application June 27, 1938, Serial No.

Divided and this application October 6, 1943, Serial No. 505,201

'23 Claims.

The present invention relates to the same general subject-matter as thatof my Patent Re. 22,272, dated Feb. 16, 1943, and in eflect constitutesan addition to or an improvement upon the subject matter of that patentin that herein are disclosed additional or auxiliary controls operableto govern the cabin pressure, yet operating at all times within theupper limits fixed by the basic differential-pressure control of theprevious patent, and within the lower limits established by the normalatmospheric pressure curve. This application is a division of myapplication Serial No. 216,028, filed June 2'7, 1938, forRate-of-pressure-change control for pressure cabins.

According to the previous invention the pressure within the cabin iscontrolled in such manner that between sea level or zero elevation and8,000 feet elevation the pressure within the cabin follows the pressurecurve of the outside atmosphere; there is no substantial differential.Between 8,000 feet and, let us say, 15,000 feet the pressure curvewithin the cabin is substantially level, that is, the pressure at 8,000feet is maintained with little or no change, though the outside pressureabove 8,000 feet is less than the pressure maintained within the cabin.A pressure differential increasing with increase of altitude is thusattained. Then from 15,000 feet up to perhaps 20,000 feet the pressurewithin the cabin is caused to drop at a rate substantially equal to, therate of atmospheric pressure drop,

such .as to maintain always a uniform differential of pressure betweenthe inside of the cabin and the outside atmospheric pressure, thedifierential amounting, for instance, to 2 /2 pounds per square inch.The pressure within the cabin follows this single line, whether theairplane is ascending or descending, and if the plane was to descendfrom 20,000 feet to sea level, the pressure within the cabin would bemaintained at the 2 pound differential, no more and no less, down to the15,000 foot altitude, then would remain substantially constant until theplane reached the 8,000 foot level, and then would closely follow theatmospheric curve from the 8,000 foot level down to sea level, or to anyintermediate point.

The present device is in the nature of a refinement of the systemdisclosed in my aforementioned patent, and relates more particularly tothe control device operable to regulate outflow from the cabin. In thepresent arrangement the absolutepressure sensitive device and theoverriding differential pressure sensitive device are cooperative intheir action, and both actupon a single valve which is the normaloutflow valve.

to inflow control, but makes itpossible to effect unified and sensitivecontrol, and the outflow valve tends to maintain cabin pressuresautomatically more nearly at desired pressures.

More specifically it is an object of this invention to minimizefluctuations in pressure from the desired values, particularly in therange intermediate the unsupercharge range and the constant differentialrange, such as between 8,000 and 15,000 feet altitude.

It is a further object to simplify and improve the control mechanismwhich is the basis of my patent mentioned above, so that betterregulation can be obtained with devices which are more sensitive andmore compact than those disclosed in such patent.

In accomplishing such objectsmy improved type of mechanism will tend todecrease hunting of the outflow valve, which would cause fluctuations inthe pressure alternately above and below the theoretical values.

. Other objects will appear hereafter, and especially such as relate tothe more purely mechanical details of my improved construction.

My invention is shown in the accompanying drawings largely indiagrammatic fashion, and the drawings and the construction-s andarrangements shown therein are to be understood in the latter sense, butinsofar as the principles thereof are concerned, the accompanyingdrawings show my invention arranged and functioning in a manner such asis at present preferred by me.

The figure is a sectional view illustrating the relationship of theparts of the control mechanism to each other and particularly theinterconnection between the absolute pressure control and the valvemoving mechanism.

The pressure control device illustrated is in general similar to thatdisclosed in my above mentioned patent, though the arrangement of thethe interior of the cabin from any suitable pressure-producing blower orsupercharging device (not shown) through a conduit 8, past a valvehaving a hollow stem 8 I, and through a Venturi throat 83. The conduit,and associated parts, constitutes a means to supply air under pressurewithin the cabin. The valve may seat at 82 to prevent further intake ofair into the cabin or to prevent escape of pressure from the interior ofthe cabin. It is movable, under the influence of a rate of flowcontrol,. by an air motor or servo device including a piston 84 movablewithin a cylinder 88, the space above the piston being capable ofcommunication with supercharger pressure in the inlet conduit 8 throughthe hollow stem 8!, and the space below the piston being incommunication with the pressure within the interior of the cabin throughthe port 95'.

Control of the piston 84, however, is under the influence of a controldevice consisting of a piston 91 within a cylinder 98, the piston 81being spring urged by a spring 88' to advance the pin 91' of the pistontowards the end of the hollow stem 8| of the valve, thereby tending toclose off the hollow stem from communication with the superchargerpressure. Movement of the piston 91 is under the influence of cabinpressure communicating with its upper side through a port 86, and apressure effect communicating with its lower side through the port 88,the latter pressure effect being made up of a reduced pressure through atube 93' from the inlet Venturi throat 93 or a reduced pressure througha tube 83' from the outlet Venturi throat 88, both communicating withthe port 89. or made up as a combination or differential of such reducedpressure from the two Venturi, throats. A valve (not shown) may beemployed at the Junction of the tubes 88 and 93 to control the reducedpressure at the port 89 under the influence of one or the other of theVenturi throats, but not both, such a valve being illustrated in myabove-mentioned patent. Its use, however, is not deemed essential in thepresent arrangement.

Air from the interior of the cabin is discharged through an outlet 8past a valve 80, capable of seating at 82 to prevent discharge from theinterior or to prevent inlet of a higher pressure from the exteriorofthe cabin, the valve 80 having a hollow stem 8|, and the air from thecabin passing through the venturi 83 prior to passing the valve seat 82and being discharged through the discharge outlet 8. It will be seenthat the interior of the hol ow stem BI is in communicatlon at all timeswith the outlet 8, constituting a region of air pressure relatively lowas compared to cabin pressure, and which air pressure is variable withand substantially equal to external atmospheric pressure.

Movement of the valve 80 may be accomplished under the influence of anair motor or servo device, including a movable servo element, such aspiston 84, received within a cylinder 8! and dividing it into upper andlower chambers, such movable element being connected directly to thehollow stem 8i. The chamber in such cylinder above the piston 84 is incommunication with a region at an air pressure relatively low ascompared to cabin pressure. preferably at substantially externalatmospheric pressure, either through the hollow stem 8i or through apassage 13, 14, hereafter referred to. The chamber in such cylinderbelow the piston 84 is in direct communication with the cabininteriorthrough the port 85'. Since piston 84 fits loosely in cylinder88 air leaks slowly from the high pressure side past the piston to itslow pressure side, whence it is exhausted through conduit 18, 14 to theatmosphere. Movement of the valve 80 and of the piston 84 is undercontrol, directly or indirectly, of two alternatively operable controldevices, a differential pressure control and an absolute pressurecontrol, either of which may have an influence upon a pressure controlvalve pin 81 aligned with and capable of moving with stem 8i whileabutting it, and thereby closing its hollow bore and preventing flow ofair through this hollow stem from the space above the piston 84 to theoutlet 8 below valve 80. However, under certain conditions, access ofexternal atmospheric pressure to the chamber above the piston 84 maystill be had through the passage l8, M. The conditions governing thiswill appear hereafter.

Considering first the absolute pressure control device, the pin 81 maybe considered as connected to and movable with one element of suchdevice which is a ported plunger 1, movable within a cylinder 10, theport H of which is adapted to be opened or closed by recession orapproach of a pin 12, which pin element of the absolute pressuresensitive unit is moved automatically in response to changes in cabinpressure. The pin 81 need not be directly connected to the plunger ii,and preferably the connection is through mechanical advantage meansshown as a lever 88 fulcrumed at 88 adjacent one end, and with acompression spring 88 acting thereon, tending to urge the pin 81 towardsits seat at the end of the hollow bore of the stem 8!, and thereforetending to lift the plunger 1 with its hollow bore ii on the pin 12.which otherwise would close the bore Ii. Opening of the bore ll permitscommunication through the passage l8, 14 between the exterior atmosphereand the chamber above the piston 84 to reduce the pressure upon theupper face of such piston, thereby, by the differential in the pressuresacting on the pistons lower and upper sides, to raise the piston 84.However, the preselector, described in detail in my parent applicationSerial No. 216,028, is interposed between these conduits l8 and I4, andcommunicates with the atmosphere through a conduit 18 by passing theabsolute pressure control. Inclusion of such a preselector is optionalas far as the present invention is concerned, serving as a purelyauxiliary control.

Pin 12 is an element movable in response to changes in cabin pressure,being shifted by the evacuated Sylphon or bellows I! on which it ismounted, such bellows being placed where it is exteriorly affected bythe cabin pressure, and is therefore expanded or contractedautomatically by decreases or increases, respectively, in cabinpressure. A limberspring l8 urges the stem 12 towards the bore 1|, andcollapse of the bellows I8 beyond a given point isprevented by a stoppin 11. Block I then constitutes a movable element cooperating with pin12.

The function of the absolute pressure control device Just described isto prevent appreciable further drop in pressure'beyond a given point,and to maintain the pressure within the cabin substantially constantduring the reduction in pressure in the surrounding atmosphereaccompanying climbing of the aircraft to a higher altitude. In otherwords, it functions to maintain a substantially constant cabin pressurebetween 8,000 feet and 15,000 feet. However, the absolute pressurecontrol is overruled by the differential pressure control when apredetermined differential: of pressure between the interior cabinpressure and the external pressure has been attained, in order that thestructure of the aircraft may not be strained by a pressure differentialgreater than that for which it is designed.

The differential pressure control will now be described. A piston 8 ismovable within a cylinder 80 in alignment with and surrounding the pin81. The piston 8 may engage a shoulder 81' on the pin 81 to lift the pin81 from the end of the hollow stem 8|, and the movement of the piston 8in this direction is resisted at first by the limber compression spring8i, and, after engagement with shoulder 81, also by spring 88 acting onlever 88. The space beneath the piston 8 is in communication with thecabin pressure through the port 82, and the space above it is incommunication with the atmosphere through the conduit 88..

It is not possible to maintain the pressure within the cabin at sealevel pressure or at any selected constant pressure level for allnecessary or feasible flight altitudes, nor indeed is it economical tomaintain a pressure within the cabin which exceeds the external pressureby more than a predetermined difference, say 2% pounds per square inch.Since it is unnecessary for various reasons to effect supercharging ofthe cabin at altitudes below 8,000 feet, or some altitude in thatvicinity, the actual pressure within the cabin for any given altitudemay be substantially equal to the external pressure at such altitude forall altitudes between sea level and 8,000 feet. However, if flight is tobe maintained at an altitude between 8,000 feet and, let us say, 15,000feet, it is desirable and possible to maintain the pressure betweenthese limits of altitude substantially constant, the differentialbetween it and the external pressure varying. To build up suchdifferential between cabin and external pressure it is necessary toaccomplish closing movement of valve 80 during operation of theabsolute-pressure control for constant flow of air through the cabin,and ultimately to place in command the differential-pressure control,after which the opening of the valve remains substantially unchanged forconstant flow through the cabin despite further increase in altitude anddecrease in atmospheric pressure.

At altitudes above the 15,000 foot altitude which has been selected, itis .not practical nor economical to maintain a constant pressure, and itis not harmful to permit the pressure to drop somewhat, and thereforethe differential pressure control serves to maintain the acquireddifferential of cabin pressure over external pressure up to 20,000 feetelevation. At this point it may be assumed that the characteristics ofthe particular blower or supercharger being employed to supply airthrough the passage 8 are such that its limit has been reached, and itcan no longer maintain the predetermined differential. If the aircraftproceeds to a higher elevation, the internal pressure will tendincreasingly to approach the external pressure.

The position of parts for supercharged operation which is automaticallyinitiated upon the attainment of a critical altitude, selected as 8,000,feet, is shown in the drawing. At such altiiency of the bellows itself.Upon expansion of this absolute-pressure sensitive device in an upwarddirection in the drawing. metering pin 12 carried by it is moved torestrict the flow of air through the orifice 1| in the slidable plug 1,which is interposed between the inlet and outlet portions of tube 18.This restricts the flow of air from the upper side of piston 84 throughthe orifice 1|, and thus tends to equalize the pressure across thepiston 84.

The outrush of air past the valve at all times tends to draw this valvedownward to its seat. and to draw the connected piston 84 downward. Upto now (below 8,000 feet)'the Sylphon 18 has been collapsed, and thespace above the piston 84 has been in communication with reducedatmospheric pressures through 18, 1|, and 14, thereby tending to balancethe outflow: downward tendency, and, with the resistance of cabinpressure, acting beneath the piston 84, -to downward movement, thepiston and valve 88 are held in their upper position, with the valveopen. Now, however, the expansion of the Sylphon 18 has reduced thepressure differential acting to hold the valve up, as described. Theaction of outfiowing air on the valve now tends to close it, since thebalancing force through 18, 1|, 14 is interrupted and in part destroyed.Nor can this balancing force be restored at this time through the hollowstem 8i, for the pin 81 follows downward movement of the piston 84,under the influence of spring 89, and prevents access of reducedexternal pressure to 'the space above the piston through the alternativepassage formed by the hollow stem 8i.

Closing movement of the valve, unless accompanied by preciselycorresponding reduction of pressure of the inflowing air to the cabin,which does not ordinarily occur, increases the cabin pressure. This inturn causes recompression of the bellows 18 and reopening of the orifice1i to the passage of air from the upper side of the piston 84, whichresults in the reopening of the valve 80 and a consequent reduction ofcabin pressure. It is clear that this .action would result in arepetitious cycle of instability wherein the valve would hunt and thecabin absolute pressure would oscillate between values slightly aboveand slightly below the preselected critical value-at which the bellows15 is expanded sunlciently to begin to close orifice 1i.

This undesirable effect can be overcome by coordinating the movements ofthe outflow valve 80 and absolute pressure unit valve 12 by mechanismoperatively interposed between them, including the linkage connectingplunger 81, abutting the hollow stem 8| of valve 80, to the orificeblock 1, including rocker arm 88, the fulcrum of which is at 88, and thepivots at its opposite ends. The ratio of the parts into which therocker arm is divided by this fulcrum is such that the plunger or pin 81can follow the valve downward accompanied by relatively slight upwardmovement of block 1. As the difference in cabin pressure over externalpressure increases, the valve must close increasingly, accompanied bycorresponding movement of the pin 81, as stated. If bellows 18maintained its control action without any further expansion whatever thecabin pressure would remain precisely constant over the increase inaltitude of the airplane from 8,000 to 15,000 feet, during which rangethe absolute pressure device is in control. Upward movement of orificeblock 1 as pin 81 follows the valve downward, however, requires bellows18 to expand in order to maintain restriction of the orifice H by pin12, and such expansion can only be effected by a corresponding decreasein cabin pressure.

Assuming that the inflow to the cabin remains substantially constant,therefore, and that the cabin leakage is-negligible, closing movement ofvalve 88 at all times bears a definite and uniform relationship to theincrease in differential of cabin pressure over the surroundingatmospheric pressure. On the other hand, expansion of bellowscorresponds directly to decrease in cabin pressure. As long as pin 81seals the aperture through stem 8i, therefore, lever 88, which directlyinterconnects valve 80 and bellows orifice block 1, controls therelative expansion of the bellows and closing of the valve, and hence,for a given increase in altitude, coordinates the incremental drop incabin pressure with the incremental increase in the difference of cabinpressure over atmospheric pressure, or degree of supercharge. Since theincrease in such pressure differential is the difference between theatmospheric pressure drop and the drop in cabin pressure, theincremental drop in cabin pressure is also uniformly related to thedecrease in atmospheric pressure, and the same is true for an increasein both pressures.

It is evident that change in the location of fulcrum 88 along lever 88will vary the ratio of movement between valve 80 and orifice block I.Consequently the position of such fulcrum may be selected or altered asnecessary to achieve the desired relationship between the incrementaldecrease in cabin pressure and the incremental increase in thedifference of cabin pressure over atmospheric pressure, for a givenascent of the aircraft, as long as the absolute pressure controlgoverns. Obviously if fulcrum 88 is moved to the left the expansion ofbellows 18 will be correspondingly greater and the closing movement ofvalve 88 correspondingly less, so that a greater drop in cabin pressurewill occur. I prefer, however, that the fulcrum be located sufficientlyfar to the right to prevent a drastic decrease in cabin orifice ii, itwill be recognized that the cabin pressure over the intermediate rangewould be precisely constant if orifice block i remained fixed. Thatmight be accomplished by locating the-fulcrum of lever 88 in itslimiting position, coincident with its connection to block 1, or,indeed, entirely separate from the block, so that only pin 81 would movewith it. Moreover an actual increase in cabin pressure as the aircraftascends would result if pivot 86 were located on the opposite side ofthe connection of bar 88 to block I. In such event, as pin 81 followedthe valve downward, orifice block 1 would be moved downward through arelatively small distance, but sufficient to restrict orifice 1i so thatvalve 80 would tend to close still further. The increase in cabinpressure thus induced would effect sufiicient collapse of bellows 15 torestore the degree of, opening of orifice I i to place the valve, leverand orifice block again in equilibrium, but at an increased cabinpressure. Such an arrangement, however, would cause excessiveovertravel, and consequent hunting of the valve.

With the preferred arrangement shown in the drawings, as valve closes inresponse to expansion of the bellows iii the orifice block i iswithdrawn slightly from the metering pin 12, thus tending to reopen thepassage ii and to check the downward travel of the valve 80. Conversely,as the valve opens to relieve superfluous air from the cabin the orificeblock I descends upon the metering pin 33, and thereby restricts theflow of air through passage H from the upper side of the piston 84, andchecks the upward travel of the valve 80. It can thus be seen that asthe valve begins to move in either direction inresponse to change incabin absolute pressure there is an immediate counter effect whichopposes such mo-. tion and prevents overtravel oi the valve. The resultis that the position of orifice ii and metering pin 72 relative to eachother is so maintained.

as to meter the fiow of air from the upper side of piston 84, andthereby cause valve 80 to seek a stable position. Closure of the valvetherefore proceeds slowly and regularly, in accordance with change ofexternal pressure, and at a rate (coupled with control of infiow,described hereafter) to maintain a substantially constant pressurewithin the cabin.

Since the stable position of the valve for a given altitude may varyconsiderably with changes in the ventilating rate, differentialpressure, or in cabin leakage conditions, the linkage between pin 87 andorifice plunger 1 is so arranged that the travel of the valve isconsiderably greater than that of the orifice in the particularinstallation pictured, as shown, approximately twelve times. In this waythe .position of the orifice ii and the critical cabin absolute pressurewhich the unit tends to maintain are neither appreciably altered by anyresponsive movement of the valve.

It is evident that the arrangement of pin 12;

maintain the cabin pressure substantially constant.

At 15,000 feet elevation the differential-pressure control is broughtinto operation, overruling the absolute-pressure control, andthereafter, for increase in altitude, maintaining the cabin pressure ata constant differential above the external atmospheric pressure. thepressure in the space above the piston 8 has decreased, due to decreasein. the external atmospheric pressure, while the pressure in the spacebeneath the piston 8 has remained substantially constant, being incommunication with the cabin pressure. The differential thus built up atthis point overcomes the-limber spring 8i, which may be adjusted toregulate the point of initiation of differential pressure control, andthe piston l rises, or tends to rise, and eventually the piston 6engages the shoulder 81' and lifts or tends to lift the pin 81 from itsclosure of the hollow stem 84; The pressure differential between thebottom and top of the piston 8 in addition overcomes the resistance ofthe spring 88 as well as that of the spring 18.

The tendency of the pin 81 to rise from the Thus at such elevationhollow bore of stem 8| tends to decrease the pressure above the piston84, whereas the pressure beneath it is substantially the same as it wasimmediately prior to lifting of the pin. The piston 84 therefore tendsto rise and to lift the valve 80 farther from its seat 82, and thus toincrease the rate of outflow of air from the interior of the cabin,thereby decreasing the pres sure w thin the cabin, but controlling therate of decrease so that the cabin pressure remains always at thepredetermined differential above the external pressure. outfiow throughtheventuri 83 tends to affect the position of the valve 90'correspondingly, so that the rate of inflow of replacement air iscontrolled in accordance with the rate of outflow to maintain thepredetermined pressure differential within the cabin, as is describedmore fully in my previously mentioned patent. This condition would holdindefinitely if the blower were of sufiicient capacity to supply therequired pressure.

Overtravel of the valve is prevented by the fact that, as contactbetween the pin 8'! and the stem 8i is broken by the action of thedifferential n pressure'control, the valve assembly follows-the pinupwardly, and tends to restrict the entry of air into the bore of thestem. It is thus evident that an immediate resistance to further motionaccompanies any increase in the lift of the valve in response to actionof the differential pressure control, and that there will be no tendencyfor the valve to hunt, or for cabin pressure to fluctuate. Theabsolute-pressure sensitive device I! will extend toward its full upwardtravel as cabin pressure is lowered accompanying an increase inaltitude, so that the passage of air through the orifice H is virtuallyeliminated by entrance into it of pin 12, having a close sliding fittherein. Such expansion of bellows 16 therefore cannot tend to liftblock 1 and force lever 88 to move pin 81 to close the orifice in valvestem 8! or press valve 80 downward, because pin 12 cannot press againstblock I.

In all the above it will be observed that the pressure within the cabinin no case decreases below the external atmospheric pressure, becauseobviously this is impossible even during a descent, as long asreplacement air is being supplied to the cabin, unless means areprovided for evacuating the interior of the cabin. On the other hand,none of these pressures exceeds the selected limit of 2 /2 poundsdifferential over and above the atmospheric pressure. Of course, all thefigures used in the above illustrations are arbitrary, and if thestructure is intended to withstand a higher differential of pressure,then the selected differential or pressure limit, whatever that limitmay be, is not exceeded, because as that differential pressure limit isattached, the differential pressure control will overrule the absolutepressure control and insure that the predetermined differential is notexceeded. This is a safety measure and prevents the imposition of unduestresses upon the structure.

I claim as my invention:

1. Mechanism to regulate aircraft cabin pressure. comprising a valveopenable for outflow of air from the cabin, spring means biasing saidvalve to close, servo means operatively connected to open the valve inopposition to said spring means, and control means sensitive to adifferential pressure varying in response to variations in thedifference of cabin pressure over ambient atmospheric pressure,operatively associated Change in the rate oi" 7 with said servo meansand operable to-remove the biasing action of said spring means on saidvalve and to effect actuation of said servo means to exert a valveopening force on said valve automatically in response to an increase inthe differential of cabin pressure over'ambient atmospheric pressureexceeding a selected value.

2. Mechanism to regulate aircraft cabin pressure, comprising a valveopenable for outflow of air from the cabin, spring means biasing saidvalve to close increasingly to increase the differential of cabinpressure over ambient atmospheric pressure for substantially constantquantity flow of air past the valve, servo means operatively connectedto open the valve in opposition to said spring means, and control meanssensitive to a differential pressure varying in response to variationsin the difference of cabin pressure over ambient atmospheric pressure,operatively associated with said servo means and operable to remove thebiasing action of said spring means on said valve and to effectactuation of said servo means to arrest closing movement of said valveautomatically in response to an increase in the differential of cabinpressure over ambient atmospheric pressure exceeding a selected value.

' ciated with said servo means and operable to remove the biasing actionof said spring means on said valve and to effect actuation of said servomeans to exert a valve opening force on said -valve automatically inresponse to an increase in the differential of cabin pressureoverambient atmospheric pressure exceeding a selected value, and absolutepressure control means sensitive to cabin pressure, operativelyassociated with said servo means and operable to actuate the same .toclose the valve increasingly with decrease in atmospheric pressure toincrease the differential of cabin pressure over atmospheric pressurewithin the selected limiting value of the differential pressure of cabinpressure over exterior pressure.

4. Mechanism to control the pressure within an aircraft cabin whereintoair is supplied under pressure, comprising a valve openable for outflowof air therepast from the cabin, servo means operatively connected tomove said valve, including a movable element, means subjecting one sideof said element to cabin pressure, the other side of said element beingexposed to a chamber, means connecting such chamber to the aircraftcabin and to a region at a pressure lower than cabinpressure, for flowof air through such chamber from the aircraft cabin to such region oflower pressure, and means automatically responsive to changes in cabinpressure and operable to control such flow through said connecting meansto govern the pressure in such chamber, thereby to alter the pressuredifferential acting upon said movable element of said servo means, thusto vary the degree of opening of said valve.

5. In a cabin pressure control, 'a valve openable for flow of airthrough the cabin, servo means operatively connected to move said valve,an absolute pressure responsive means including an evacuated bellowssubject externally to cabin pressure, a shiftable block member having anorifice therein, means defining a passage communicating between theorifice of said shiftable block member and said servo means, a valvemember cooperating with the orifice in said block member and shiftablerelative thereto to control the effective size of the orifice forregulating the flow through said passage means, and hence the pressureto which said servo means is subjected, one of said members beingoperatively connected to said bellows for movement therewith, and alever connected to the other of said members relatively close to thelever fulcrum, and operatively engaged with said cabin air flow valverelatively far from the lever fulcrum for movement therewith, to effectrelatively slight movement of such other member corresponding torelatively large movement of said cabin air flow valve.

6. In a cabin pressure control, an outflow valve biased to close, astem, and a pressure movable servo member, all operatively connected,said servo'member dividing a space into a high and a low pressurechamber, passage means directly interconnecting the high pressurechamber and the cabin to establish cabin pressure in such chambertending to open the valve, and providing bleeding of substantially cabinpressure air into the low pressure chamber, two passages alternativelyconnecting the low pressure chamber with a source of pressure lower thancabin pressure, control valve means in each such passage, anabsolute-pressure responsive means subject to cabin pressure,operatively connected to regulate one such control valve means, tomaintain cabin pressure elevated above external pressure, and adifferential pressure responsive means subject to cabin pressure and toexternal pressure, operatively connected to regulate the 'other suchcontrol valve means, to prevent cabin pressure exceeding externalpressure by more than a selected value.

7. A cabin pressure control as in claim 8, wherein the absolute pressureresponsive means and its associated control valve means comprises anevacuated bellows subject externally to cabin pressure, a needle valveelement, and a cooperating orifice block element shiftable axially ofand relative to the needle'valve element to control the effective sizeof the orifice and the low pressure force effective upon the servomember, one of said elements being operatively connected to the bellows,and follow-up means operatively connecting the other of said elements tothe outflow valve.

8. A cabin pressure control as in claim 6, wherein the differentialpressure responsive means and its associatedcontrol valve meanscomprises .a follower stem arranged for follow-up movement with and withrelation to the outflow valve's stem, one of such stems being hollow andconstituting a part of the corresponding low pressure passage, and theend of the other stem constituting a valve for the hollow stem, a springloaded piston subject, on one side to cabin pressure and on its otherside to external pressure, and stop means interengageable between thepiston and the follower stem, following predetermined movement of thepiston due to increasing differential of pressure, to shift the followerstem away from the outflow valve stem, and thereby to open the passagethrough the hollow stem to increase the {pew pressure force effectiveupon the servo mem- Q. A cabin pressure control as in claim 6, whereinthe absolute pressure. control and its able orifice block, arranged inthe corresponding passage, and a cooperating registering and shiftablemetering pin arranged to close the passage through the orifice block toa greater or lesser degree, an evacuated bellows subject externally tocabin pressure, and operatively connected to shift the metering pin, andmeans reacting from the outflow valve to effect follow-up shifting ofthe orifice block.

10. A cabin pressure control as in claim 6, wherein the diflerentialpressure control and its associated control valve means comprises acylinder and a piston therein arranged coaxiaily with the outflow valvestem, the piston being subject to cabin pressure at one side and to external atmospheric pressure at its opposite side, a spring resistingmovement of'the piston, and yieldable under a selected pressuredifference, a follower stem penetrating the piston and its cylinder, andengageable by the valve's stem, one such stem being hollow and alsocommunicating with the external atmosphere, the other stem cooperatingtherewith to nearly close off the adjacent end of the stem hollow, and ashoulder on said follower stem engageable by the piston when the'springyields under the selected pressure difference, to unseat thefollower stem from the valve stem.

11. A cabin pressure control as in claim 6, wherein the differentialpressure control and its associated control valvemeans comprises acylinder and a piston therein arranged coaxially with the outflow valvestem, the piston being subject to cabin pressure at one side and toexternal atmospheric pressure at its opposite side, a spring resistingmovement of the piston, and yieldable under a selected pressuredifference, a follower stem penetrating the piston and its cylinder, andengageable by the valve's stem, one such stem being hollow and alsocommunicating with the external atmosphere, the other stem cooperatingtherewith to nearly close off the adjacent end of the stem hollow, ashoulder on said follower stem engageable by the piston when the springyields under the selected pressure diiference, to unseat the followerstem from the valve stem, and an interconnection between the followerstem and the absolute pressure control, to shift the cabin to establishcabin pressure in such chamber tending to open the valve, and providingbleeding of substantially cabin pressure air into the other of saidchambers, two alternate passages leading from such other chamber to alow pressure source, and when in communication therewith assisting toopen the valve, and two alternative pressure sensitive devices, oneassociated with each such passage, to control communication through thelatter, one of said pressure sensitive devices being responsive to thedifference of cabin pressure over external pressure, and arranged toopen its passage at a selected .dlfl'crcntial, to prevent the same beingexceeded.

l3 and the other pressure sensitive device being subject to absolutepressure. and arranged to efi'ect increase of cabin pressure overexternal pressure.

18. Mechanism to control aircraft cabin pres-- sure, comprising a valveopenable for outflow of air from the cabin. an integral valve stem, apressure movable diaphragm secured on the stem, a casing enclosing thediaphragm and divided thereby into two chambers, passage means ,directlyinterconnecting one of said chambers and the cabin to establish cabinpressure in such chamber tending to open the valve, and providingbleeding of substantially cabin pressure air into the other of saidchambers, two alternate passages leading from such other chamber to -alow pressure source, and when in communication therewith assisting toopen the valve, and two alternative pressure sensitive devices, oneassociated with each such passage, to control com- 'munication throughthe latter, one of said pressure sensitive devices being responsive tocabin pressure, and arranged to modify flow through its passage withdecrease of cabin pressure, to

create an elevated cabin pressure, and the other pressure sensitivedevice being subject to the dif- 14 closed, and control means sensitiveto a diiferen tial pressure varying in response to variations in thediflerence of cabin pressure over ambient atmospheric pressure,engageable with said stem to arrest movement thereof by said stemactuat-- ing means as said outflow valve closes, for movement of saidoutflow valve away from said stem to open such passage means regulatingvalve for flow of air through said passage means to vary the airpressure in said servo means for arresting closing movement of saidoutflow valve thereby.

16. In a cabin pressure control, a valve openableifor outflow of airfrom the cabin, a high pressure source, a low pressure source, a servoelement having one side communicating with the high pressure source andthe other side communicating with the low pressure source, and movableby a differential in the pressures produced by such pressure sources onopposite sides thereof, means operatively connecting said servo elementto said valve to move it toward open position, an absolute pressureresponsive means subject to cabin pressure, operatively connected to oneof said pressure sources to regulate the value of the differential inthe pressures acting on said elements, thereby to effect progressiveclosing ference of cabin pressure over external pressure,

,piston movable within a cylinder, a follower stem penetrating saidpiston, and disposed coaxia-ily with the outflow valve stem andshiftable therewith, one of said stems being hollow and constitutingapart of one such passage, and affording communication between the lowpressure chamber and a low pressure region, but normally nearly seatedupon the other stem to materially restrict such communication, a springof given force urging the piston downwardly, its lower side havingcommunication with the cabin pressure, whereby upon attainment of aselected difference of cabin pressure over external pressure the springis yieldab-le to permit the piston to rise, a shoulder on the followerstem engageable by the rising piston, to unseat the hollow stem, anorifice block and cooperating metering pin arranged in the alternativepassage from the low pressure chamber, an evacuated bellows subjectexternally to cabin pressure, operatively connected to shift themetering pin to create an elevated cabin pressure,

. and a follow-up connection between the orifice block and the followerstem, to shift the latter in accordance with movement of the outflowvalve under the influence of said bellows.

l5. Mechanism to regulate aircraft cabin pressure, comprising an outflowvalve openable for outflow of air from the cabin, pneumatic servo meansoperatively connected to the valve to effect movement thereof, passagemeans defining an air passage communicating with said servo means forvarying the pressure therein, a stem cooperating with said valve todefine a regulating valve in the passage formed by said passage means,actuating means normally operable to move said stem co'njointly withsaid outflow valve to maintain such passage means regulating valvenormally above atmospheric pressure, and movement 00- of said valve asthe ambient atmospheric pressure decreases to maintain cabin pressureelevated ordinating means operatively interposed between said valve and.said absolute pressure responsive means and operable to coordinateclosing movement of said outflow valve with decreasing cabin pressuremovement of said absolute pressure responsive means, and vice versa,said movement coordinating means including a member moved automaticallyin response to closing movement of said valve and to a correspondingdegree, and operatively connected to said absolute pressure responsivemeans to effect relatively slight cabin pressure decreasing movementthereof corresponding to relatively large closing movement of saidvalve.

17. A cabin pressure control as defined in claim 16, in which theautomatically moved member of the movement coordinating means is a leverhaving an eccentrically located fulcrum,

the long end of said lever being movable auto-.

matically in response to movement of the valve and to the same degree,the short end of said lever being operatively connected to the absolutepressure responsive means to move the same.

18. In an aircraft having a pressure cabin and means for delivering airthereto at greater than atmospheric pressure, a cabin pressure controlsystem comprising a valve in the cabin wall for bleeding air therefrom,a control device including an element movable in response to changes incabin pressure and a cooperating movable element, relative movement ofsaid elements governing said valve to close progressively as thesurrounding atmospheric pressure decreases with increasing altitude, tomaintain pressure within said cabin at values above the correspondingatmospheric pressures, follow-up means moved by said valve, andmechanical advantagemeans operatively connecting said follow-up meansand said cooperating movable element of said control device, andoperable by said follow-up means to move said cooperating movableelement to a lesser degree but in definite ratio tothe movement of saidvalve, said cooperating movable element, by such movement, governingsaid control device to actuate said valve for decreasing cabin pressureprogressively with increasing altitude by morements less than thecorresponding increments of decrease in surrounding atmosphericpressure.

19. Mechanism to regulate aircraft cabin pressure, comprising a valveopenable for outflow of air from the cabin, pneumatic servo meansincluding an air chamber, high pressure source means affordingcommunication between said air chamber and the aircraft cabin, lowpressure source means affording communication between said air chamberand a region at an air pressure relatively low as compared to cabinpressure, and a pressure responsive element disposed in such chamberbetween the openings of said high pressure source means and saidlowpressure source means into such chamber and operated by the air pressurechamber differential produced thereby,

and operatively connected to the valve to move therewith and to effectmovement thereof, valve mechanism operable to vary the communicationthrough said low pressure source means between said air chamber and suchregion of relatively low air pressure. including a control membernormally abuttin said valve-connected element and in such relationshipsevering communication through said low pressure source means betweensaid air chamber and such region of relatively low air pressure, andmovable relative to said valve-connected element from such abuttingrelationship to decrease the pressure within such air chamber, anddifferential pressure control means sensitive to a differential pressurevarying in response to the difference of cabin pressure over ambientatmospheric pressure, and operable to move said control member relativeto said valve-connected element from abutting relationship forestablishing communication through said low pressure source meansbetween said air chamber and such region of relativel low air pressurefor decreasing the pressure therein to exert a valve opening force onsaid valve-connected element.

20. Mechanism to regulate aircraft cabin pressure, comprising a valveopenable for outflow of air from the cabin, pneumatic servo meansincluding an air chamber, high pressure source means affordingcommunication between said air chamber and the aircraft cabin, lowpressure source means affording communication between said air chamberand a region at an air pressure relatively low as compared to cabinpressure, and an element disposed in such chamber between the openings fsaid high pressure source means and said low pressure source means intosuch chamber and operated by the air pressure chamber differentialproduced thereby, and operatively connected to the valve to movetherewith and to effect movement thereof, valve mechanism operable tovary the communication through said low pressure source means betweensaid air chamber and such region of relatively low air pressure,including a control member normally abutting said valve-connectedelement and in such relationship severing communication through said lowpressure source means between said air chamber and such region ofrelatively low air pressure, and movable relative to said valveconnectedelement from such abutting relationship to decrease the pressure withinsuch air chamber, and differential pressure control means sensitive to adifferential pressure varying in response to the difference of cabinpressure over ambient atmospheric pressure, and operable to move saidcontrol member relative to said valveconnected element from abuttingrelationship for estabiishin g cqmmunicst ion thro gh said ,low

pressure source means between said air chamber and such region ofrelatively low air pressure fordecreasing the pressure therein to exerta valve opening force on said valve-connected element, and absolutepressure control means sensitive to cabin pressure and operable tocontrol communication between such air chamber and a region of an airpressure relatively low as compared to cabin pressure, and consequentlyto control the pressure acting on said valve-connected element whilesaid valve mechanism control member is in position abutting saidvalve-connected element.

21. Mechanism to control the pressure within an aircraft cabin whereintoair is supplied under pressure, comprising a valve openable for outflowof air therepast from the cabin, servo means operatively connected tomove said valve, including a movable element, means subjecting one sideof said element directly to cabin pressure and providing bleeding ofsubstantially cabin pressure air to the other side thereof, meansestablishing communication between such other side of said movableelement and a region at a pressure lower than cabin pressure, and means.

responsive to changes in cabin pressure and automatically operable tocontrol the communication effected by such communication establishingmeans with such lower pressure region to vary the pressure on such otherside of said movable element, thereby to.alter the pressure differentialacting on said movable element of said servo means, and hence the degreeof opening of said valve.

22. In a cabin pressure control, a valve openable for outflow of airfrom the cabin, actuating means for said valve, control means operableto regulate said actuating means including an absolute pressureresponsive means subject to cabinpressure, and movement-coordinatingmeans operatively interposed between said outflow valve and saidabsolute pressure responsive means and operable to coordinate closingmovement of said outflow valve with decreasing cabin pressure movementof said absolute pressure responsive means, and vice versa, saidmovement-coordinating means including a member moved automatically inresponse to closing movement of said valve, and to a correspondingdegree, and operatively connected to said absolute pressure responsivemeans to effect relatively slight cabin pressure decreasing movementthereof corresponding to relatively large closing movement of saidvalve.

23. In a cabin pressure control, a valve openable for outflow of airfrom the cabin, actuating means for said valve, control means operableto regulate said actuating means including absolute pressure responsivemeans subject to cabin pressure, an element operated by said actuatingmeans and moved progressively in one direction as the surroundingatmospheric pressure decreases with increasing altitude, andmovement-coordinating means directly connecting said element and saidabsolute pressure responsive means and operable to coordinate movementof said element in such direction with decreasing cabin pressuremovement of said absolute pressure responsive means,

and vice versa, in corresponding degrees. and.

operatively connected to said absolute pressure responsive means toeffect relatively slight cabin pressure decreasing movement thereof byrelatively large movement of said element in such direction.

NATHAN C. PRICE.

(References on following page)- 17 7 REFERENCES CITED Number Thetollowing references are of record in the file of this patent. 2,307,199UNITED STATES PATENTS 5 2,419,707 Number Name Date Re. 22,272 Price Feb.16, 1943 N b 1,562,663 Strong Nov. 24, 1925 2 5 1,832,809 Hudson Nov.17, 1931 521'623 1,890,472 Temple r Dec. 13, 1932 I Name Date Gregg May21, 1935 OConnr Aug. 9, 1938 Cooper Jan. 5, 1943 Cooper et a] Apr. 29,1947- Y FOREIGN PATENTS Country Date France Nov. 8, 1920 Great BritainMay 27, 1940 Certificate of Correction Patent No. 2,456,215. December14, 1948.

NATHAN 0. PRICE It is hereby certified that errors appear in the printedspecification of the above numbered patent requiring correction asfollows:

Column 14, line 26, claim 16, after the word said insert servo; sameline, for elements read element;

and that the said Letters Patent should be read with these correctionstherein that the same may conform to the record of the case in thePatent Office.

Signed and sealed this 5th day of April, A. D. 1949.

THOMAS F. MURPHY,

Assistant (lommissz'oner of Patents.

